This invention relates to a welding terminal and a welding apparatus for welding the welding terminal, and more particularly to such welding terminal and welding apparatus, in which for example, an insulating sheath of a wire is removed to thereby expose a conductor portion thereof, and this exposed conductor portion is welded to a terminal base plate portion by welding or vibration welding.
A related method of connecting a welding terminal and a wire together is disclosed in JP-A-62-140308, in which a conductor portion of a wire is welded to a central portion of a welding portion of a terminal base plate by electric resistance welding, ultrasonic welding or the like, thereby enhancing the reliability of the electrical connection.
For example, as shown in FIG. 6, a welding terminal 100 of an integral construction, formed by bending an electrically-conductive sheet, includes a terminal base plate portion 101 which has an earth fastening hole 103 (serving as an electrical connection portion), formed in a front end portion thereof, and also has a pair of wire sheath-clamping portions 105 formed at a rear end portion thereof. Further, a pair of side walls 102 are formed on and project perpendicularly from opposite side edges of an intermediate portion of the terminal base plate portion 101 (serving as a welding portion), respectively, so that this portion is cross-sectionally U-shaped.
A conductor portion 108 of a wire 106, exposed by removing an insulating sheath 107 thereof, is set between the side walls 102 of the terminal base plate portion 101 serving as the welding portion.
In this condition, a vibration horn 110 is pressed against the conductor portion 108 from the upper side as shown in FIG. 7A, and this vibration horn 110 applies ultrasonic vibration to the conductor portion 108.
As a result, the cross-section of the conductor portion 108 is deformed from a circular shape into a flattened shape as shown in FIG. 7B, and at the same time, conductors of the conductor portion 108 are fused by localized vibration heat produced by the ultrasonic vibration energy.
At this time, the side walls 102 serve to prevent the conductors of the conductor portion 108, pressed by the vibration horn 110, from being loosened, thereby preventing the ultrasonic vibration energy from being less liable to be transmitted thereto. As a result, the conductor portion 108 of the wire 106 is integrally fused and fixed to the terminal base plate portion 101 of the welding terminal 100 as shown in FIG. 7C.
Therefore, the related welding terminal 100 can achieve a higher reliability of the electrical connection as compared with a press-clamping terminal in which a conductor portion of a wire is press-clamped by conductor-clamping portions formed integrally on a terminal base plate portion.
The method of welding the conductor portion 108 of the wire 106 to the terminal base plate portion 101 of the welding terminal 100 is not limited to the ultrasonic welding method, employing the vibration horn 110, but there can be used any other suitable method such as an electric resistance welding method in which the conductor portion 108 is welded and fixed to the terminal base plate portion by the use of a welding electrode.
However, as shown in FIG. 7, the pair of side walls 102, formed perpendicularly on the terminal base plate portion 101 of the welding terminal 100, are formed by bending the relevant portions at substantially right angles. Therefore, when the conductor portion 108 is pressed by the vibration horn 110 for welding the conductor portion 108 to the terminal base plate portion 101, it is difficult to press the conductor portion 108 closely into corner portions 104 formed respectively at the opposite side edges of the terminal base plate portion 101.
The vibration horn 110 fails to press the conductor portion 108 closely into the opposite side corner portions 104, so that gaps 111 are formed between each opposite side corner portion 104 and the conductor portion 108 as shown in FIG. 7C.
As a result, the ultrasonic vibration energy is less liable to be transmitted to the conductor portion 108. Even when the welding is effected in such a condition, those portions of the conductor portion 108, facing the corner portions 104, respectively, are insufficiently welded, and this has invited a problem that the strength of the joined portions decreases.
In addition, when the gap 111 is formed at the welded portion, the formation of an interfacial corrosive product is promoted at the gap 111, which leads to a possibility that the electrical connection performance is lowered. Particularly when an aluminum alloy is used as the electrically-conductor sheet for forming the welding terminal 100, the formation of such corrosive product is often arisen.